1. Field of the Invention
The present invention relates to integrated circuits, and more specifically to a signature generator circuit for checking the validity of data.
2. Description of Related Art
The principle of integrated circuit transponders is to allow a reader to check the transponder and/or leave a trace in the transponder with minimum handling (it is enough for the transponder to be in the vicinity of a reader). Generally, the transponders are small-sized objects (credit card-sized badges, tags, or car keys) and they are not provided with an independent power source. To operate, the transponder is provided with a small antenna that picks up a modulated magnetic field. An integrated circuit connected to the two terminals of the antenna produces a supply voltage from this field and then demodulates and/or modulates the magnetic field to communicate with the reader.
Various problems arise in integrated circuits designed for use in transponders. The integrated circuits have to be small so that they can be placed in different objects without being destroyed by mechanical deformations of the object in which they are placed. Also, the consumption of the integrated circuits must be reduced to a minimum because the received supply does not make it possible to obtain a great deal of power. A greater problem arises in the transmission of data. Indeed, the data is modulated on a magnetic field that may be noise infested in varying degrees.
Furthermore, the constraints on size and consumption of the integrated circuit do not allow for a complicated error correction device. There are known ways of using a double check on parity. The double check on parity consists in checking the parity of each transmitted word and in checking a parity signature on a certain number of successively transmitted words. However, better error detection in transponder integrated circuits is desirable.